Roasting sulfide ores



July 6, 1954 w. K. I Ewls ROASTING SULFIDE CRES Original Filed June 2, 1947 :50i/e raton* boQmN dHAMbaQ IQIN ET L- x:@z

@ W @ttorae Paieid July 6, 1954 ROASTIN G SULFIfDE- ORES Warren K. Lewis, Newton,- Mas's'., assigno'r to Standard Oil Developmentr Company, a corporation of Delaware Continuation of applicationA Serial@ o. '75E-1,180, June 2,v 194:7.` This applctiil Jl'1h`e 12, 1952,

Serial No. 293,051

3 Claims.

l This application is a continuation of Serial No. 751,780 led June 2, 1947, now Patent No` 2,537,629 dated May 5, 1953.

The present invention is directed to a method for roasting sulfide ores, particularly pyrites.

In the roasting of sulde ores, ci which pyrites is the most commonly employed, for the production or" SO2 for use as such or for conversion to its salts, the principal objective is to produce a gas substantially free from S03, excess oxygen and sulfur vapor. Sulfur vapor, if contained in the final product, condenses on coolingsurfaces when it is sought to liquefy the SO2 and interferes with cooling. to S03 when the SO2 is dissolved in aqueous solution as such or in the form of sultes or bysuliites. Hitherto difficulty has been encountered inachieving this objective.

The principal object of the present invention is the provision of a method for producing'fromy sulfide ores SO2 substantially free from S03, free oxygen and elemental sulfur.

Another objective in the roasting of sulfide ores is the complete recovery ofthe sulfur fromv the ore. 1n the case of pyrtes, this is particularly important because the presence or residual sulfur in the cinder renders the latter unusable for many purposes, for example, as charge to an iron the'sulde ore is processed in lnely divided' form.' It is` preferred that the ore be groundv to a size"- such that substantially all of it will pass through 1'00 mesh screen. Forthe best performance the groundore should include a wide range of par-r ticle Vsizes rang-ing upwardly from about 20" microns toY about loo mesh with Va large properu tion of material between about 200 and 490 mesh. l'n essence, the method of the present invention resides in the processing of the ore'in stages, the initial distillation and partial oxidation 0c- Ici'i'rringfirra first stage with the finely ground ore inY aguidized condition", the residual partially oxidized ore being further oxidized in a second stage, again in a iiuidized condition so as to bring the sulnd'e content down to a very low level, and the residual oreirorn this stage being subjected to a cleanfup stage. It is a feature of the' present invention that the oxidation ofthe vaporiaed sulfur from the initial ore is substantially segregated from the distillation step propen Excess oxygen oxidizes SO2 Y slater-ing. temperatures are avoided at all' poi-nts where s'olidsla're present.

Other featuresA of the present invention will be evident from the following detailed description ofthe accompanying drawing in which the singlen figure is a front elevation in diagrammatic forrlifA of a plant suitable for the practice of the present invention.

Referring to the drawing in detail, numeral l designates a hopper for' ground sulde ore havinga'drop'l'eg 2 which dischargesinto the bottom portion' of a vessel 3' which may be termed a distillation. zone. The drop leg. is provided. with a suitable feed control valve d andrmay also b'e provided with suitable aeration jets so as to maintain the powdered'v material therein in an aerated condition.

They vessel 3 is provided near its bottom, preferably belowl the point of entry of the drop leg 2, with a grid or grate 5` below which is an inlet line 6' for air, pure oxygen, or oxygen-enriched gas; At its upperend the-vessel 31 is provided with an internal cyclone l having a dip leg 8 which termina-tes at a point in the reactor where the solid is present in the form of a denseA suspension. To achieve such a suspension, the Velocity of the gasA introduced through line 6 through the vessel ismaintained at a value between about 1/5 and 5 it./second, preferably about l. and 3 ft./second. At velocities in this range the powdered material exists the-form of a dense, iiuidized suspension having a definite upper level such as indicated-by S. By dense is` meant a suspension containing at lea-stesi by volume of solid, and, preferably, be-

tween 10 and 25% by volume of solid. The exact density of the suspension will depend on the rate of feed of the solid as Well as on the velocity of the gas. 1 With enough solid in' the zone to provide a'V given densityv at a given velocity, this denfrom' the dense phase into the drawoff. Suitable aerating jets Ilv are provided along the duct lt'v to maintain the material therein in an aerated condition.

Vessel 3 is also provided with an internal vcoil I2' through which may be circulated a Ycooling medium suitably selected with regard to the temperature to be maintained in the vessel 3. It will be understood that other forms of heat exchange devices may be employed and that a simple coil is depicted for illustrative purposes only.

Air or other oxygen-containing gas enters the system at several points. One of these points is designated by i3. Gas from this point of entry supplies the inlet 6 and, by suitable manipulation of valve i4, also helps to supply line I5 which discharges into a line which is a continuation of drawoff duct lil. By suitable manipulation of valves l and Il air from this source may also be divided between inlet line 6 and line i3 which connects with a line i9 conducting gas from the upper end of vessel 3 to an upper burning chamber 2e. A supplemental supply of air or other oxygen-containing gas may be introduced into the system at this point through line 2l.

The chamber 2i! may assume any desired form and may be, as shown, iilled with packing 22 such as Raschig rings, ceramic balls, or the like, resting on a grate or grid 23. It is preferred that the gases entering chamber 2li pass through a mixing device 2li so as to insure thorough mixing of the components.

Combustion gas leaves the upper end of burning zone 2E! through a line 25 which passes through a heat exchanger 26 and thereafter connects with line l5 through valve 21.

The iiuidized solid leaving vessel 3 through duct il] passes through a continuation of this duct, in which its movement is facilitated by gas entering through line I5, and discharges through a funnel-shaped member 28 covered with a suitable grid 2e 'into a vessel Sil, which may be similar in construction to vessel 3. This vessel is also provided with internal coo-ling means represented by coil 3i and with an internal cyclone 32 having a dip leg 33 extending 4below the level 34 of the suspension of uidized solid maintained in this vessel. Gas leaves the upper end of this vessel through a line 35 which passes through a heat exchanger 3e and thence to storage or t0 recovery apparatus in which it is further processed.

Solid material leaves the bottom of the vessel 3G through a star feeder 3l which discharges the solid into the upper portion of a vessel 38. This is a clean-up vessel in which residual sulfur is removed from the ore. In the embodiment shown, this vessel is filled with packing 39- in the form of Raschig rings, ceramic balls, or the like, resting on a grate or grid lid. Iot air or other oxidizing gas is fed into the bottom of this vessel through line iii which receives this gas from a loop s2 which includes both preheaters 25 and and which receives fresh gas through line 43.

Vessel 353 is also provided at various levels with cold air inlets 135. Gas leaves the upper end of vessel 36 through line t5 and may be conducted by suitable manipulation of valve 46 through vessel 3c or, by suitable manipulation of valve 47 and valve 4%, to line i8. It will be understood that part of this gas may, if desired, be caused to pass through vessel 3. Residual FeaOs is removed from the bottom of vessel 38 through bottom drawoff line ile.

The first thing that happens when FeSz is heated is distillation of half the sulfur. The burning of this sulfur is difficult in that it must be completely mixed with air and even then oxidation to SO2 is relatively sloW unless the temperature level is very high. Modern sulfur burner design provides for these conditions, but excess air is always required for complete combustion and some S03 formation results. In a pyrites roaster much sulfur oxidation together with oxidation of FeS occurs at or near the point of distillation of the sulfur. The high heats of reaction cause high localized temperature, resulting in well recognized sintering difficulties. The system of the present invention segregates nal sulfur vapor oxidation from the distillation zone but furnishes the heat of distillation by partial combustion of sulfur Vapor and o-f FeS in vessel 3.

In the operation of the present invention, all distillable sulfur is removed from the solid in vessel 3. In order to insure this result enough air is fed upwardly through the vessel to burn some of the Fes to FeO, thereby providing heat for the distillation of sulfur from FeSz. As a feature of the invention, the duct IU together with its connecting pipe are sufficiently long so that if there is any FeSz left in the solid leaving vessel 3 it will react with the F'eO contained in the solid to produce FeS and SO2. Thus, it is desirable to conduct the operation in vessel 3 so that some FeO will be formed and to maintain at least in the duct lil a sufficiently high temperature to support the reaction between FeSz and FeO. The completion of this reaction in the duct prevents the entry of FeSz into vessel B and the sublimation of sulfur from this vessel.

The temperature in Vessel 3 should be maintained below 2000 F. and preferably below 18:39o F by suitable removal of heat by the indirect heat exchanger. 'Ihe maximum temperature permissible in this vessel is justbelow that at which the ore will sinter.

Sufficient air or other oxygen-containing gas is fed to burner 20 to assure complete oxidation of all distilled sulfur. This requires some excess oxygen and introduces some S03 into the off-gas from burner 2li. High combustion temperatures can be used in burner 26 because there is no solid present in this vessel to sinter other than whatever packing which may be employed which Will be suitably selected to withstand whatever temperature is maintained. The gas leaving the burner 20 contains oxygen, SO2, S03 and nitrogen, if air has been employed. This gas should contain at least 2% by volume of oxygen and preferably more than 5%. rIhe oxygen content of this gas can be regulated -by controlling lthe feed of oxygen-containing gas to burner Zt.

The solid passing from vessel 3 to vessel 36 is primarily a mixture of FeS and FeO. Vessel 30 is also maintained at a temperature below 2000 F. and preferably below 1800 F., the toptemperature again being regulated by the sintering temperature of the ore. The composition of the solid mixture passing from vessel 3 to vessel 33 is controlled by regulating the supply of oxygen-containing gas to vessel 3. The gas recovered from vessel 3S is primarily sulfur dioxide, mixed with nitrogen, if air has been employed.

The solids passing from vessel 30 to vessel 36 will consist primarily of FeO with a small but denite amount of Fes. This content of FeS is deliberately preserved in vessel 30 so as to preclude the formation of S03 in this vessel. Its presence also insures that the off-gas from vessel 39 will be free from oxygen.

In vessel 38 the last traces of sulfur are removed from the solids. To achieve this, strong oxidizing conditions must be maintained, that is, oxygen in excess of that required to carry the FeO to FezOa. Therefore, some S03 will be formed in addition to SO2.. The temperature in this vessel must be high, limited only by the sintering temperature of the solid. The oxidizing gas and the solids in vessel 38 should pass countercurrent to each other and this may be assured by providing packing in this vessel. In order to prevent run-away of temperature in this vessel, cold air may be introduced through the inlets 44 at spaced points. In fact, most of the air will be introduced at these spaced points. The quantity of air entering at the bottom is relatively small in amount but should be hot in order to strip all sulfur compounds from the FezOg cinder. The temperature of this air entering the bottom should be at least 1500 F. and preferably above 1800 F., the maximum being the fusion point of the cinder.

It will be apparent that thepresent invention is susceptible to considerable change without suffering any essential change in character. Wherever packing hasv been recommended in the processing of solids, it will be apparent that trays and bubble caps with downcomers can be used as an alternative. Considerable control of the process has been made possible by the various connections from vessel to vessel permitting adjustment of the composition of the gas passing through any particular vessel. It will be understood that the vessels do not have to have the exact relationships shown so long as the sequence of operations is substantially observed. While vessels 3 and 30 have been illustrated as the bottom drawoi type with internal cyclones, it will be apparent that the operations in these vessels can be so conducted that the solids pass off overhead to external cyclones or other suitable separators for solids and gases.

The nature and objects of the present invention having thus been set forth and a specic illustrative embodiment of the same given, what is claimed and desired to be secured by Letters Patent is:

1. In a process for roasting iron suliides with a free oxygen-containing gas the improvement which comprises, continuously introducing into a reaction zone a suspension of finely divided iron sulide in a free oxygen-containing gas into a bottom portion of a dense turbulent iuidized bed consisting predominantly of hot iinely divided iron oxide whereby the sulfide is oxidized and SO2 produced, indirectly cooling the contents of the fluidized bed by circulating a cooling fluid through a cooling coil immersed in said bed, removing overhead from the reaction zone a gas containing SO2, and continuously separately removing solids consisting substantially of iron oxide with small amounts of iron sulfide from `a bottom portion of said reaction zone below the point of introduction of the suspension.

2. A process according to claim 1 in which the free oxygen containing gas is air and in which the temperature in the reaction Zone is maintained below 2000c F.

3. A process according to claim 1 in which the suspension introduced into the reaction zone also contains small amounts of FeO.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,031,504 Rhodin Feb. 18, 1936 2,367,351 Hemminger Jan. 16, 1945 2,409,707 Roetheli Oct. A22, 1946 2,419,245 Arveson Apr. 22, 1947 2,445,327 Keith July 20, 1948 2,506,317 Rex May 2, 1950 2,591,595 Ogorzaly Apr. 1, 1952 FOREIGN PATENTS Number Country v Date 587,974 Great Britain May 6, 1947 

1. IN A PROCESS FOR ROASTING IRON SULFIDES WITH A FREE OXYGEN-CONTAINING GAS THE IMPROVEMENT WHICH COMPRISES, CONTINUOUSLY INTRODUCING INTO A REACTION ZONE A SUSPENSION OF FINELY DIVIDED IRON SULFIDE IN A FREE OXYGEN-CONTAINING GAS INTO A BOTTOM PORTION OF A DENSE TURBULENT FLUIDIZED BED CONSISTING PREDOMINANTLY OF HOT FINELY DIVIDED IRON OXIDE WHEREBY THE SULFIDE IS OXIDIZED AND SO2 PRODUCED; INDIRECTLY COOLING THE CONTENTS THE FLUIDIZED BED BY CIRCULATING A COOLING FLUID THROUGH A COOLING COIL IMMERSED IN SAID BED, REMOVING OVERHEAD FROM THE REACTION ZONE A GAS CONTAINING SO2, AND CONTINUOUSLY SEPARATELY REMOVING SOLIDS CONSISTING SUBSTANTIALLY OF IRON OXIDE WITH SMALL AMOUNTS OF IRON SULFIDE FROM A 